Terpenes are natural solvents existing both in the citrus fruits and in many other plants, with extraordinary technical and chemical properties. Terpenes include any hydrocarbon of the formula C5H8 and are derivable chiefly from essential oils, resins, and other vegetable aromatic products. Many terpenes are acyclic, bicyclic, or monocyclic, and differ somewhat in physical properties. They can represent an optimal alternative to halogenated solvents in many civil and industrial applications.
Nearly all the terpenes, contained in the essential oils of many plants, are constituted by a skeleton of carbon atoms made of isoprene (C5H8) units regularly linked according with the head-tail position. Some components are shown in the following formulas. The main component of the essential citrus fruit oil is d-limonene, commonly called dipentene, a hydrocarbon insoluble in water. When the essential oils are used to flavor something, it's necessary to bring them in a very thin suspension in the aqueous product (soft drinks, juices, etc.). Terpenes are typically environmentally safe and can reduce the environmental impact in many applications related to the organic solvent use.
U.S. Pat. No. 5,814,376 issued on Sep. 29, 1998 to Michael D. Cabelli teaches a gravure coating process for producing electroconductive polymer films. The coating is for use in sensors detecting analytes and the final product is heated. The above patent is limited to a ribbon-like or flat substrate application. The above uses a conductive polymer and exposing it to a dopant thereby changing its properties in situ. By changing it's properties they teach that it can be used as a component in a measuring device. This patent does not teach the use of terpenes with conductive polymers for corrosion inhibition. Ideally, in the present invention, once used or applied, the polymer will not be changed, modified or doped. The polymer will continue to perform (prevent corrosion) if it remains in a constant state. While the details of the mechanism for corrosion protection/inhibition has not been published for conductive polymers, it is likely to be a passivation of the metal substrate or an ability to allow electron transfer between the coating and substrate to prevent localized charge buildup at a metal surface, thereby eliminating corrosion. By preventing a localized charge buildup at a metal surface or between two surfaces that have different oxidation potentials, it's likely that the conductive polymer inhibits the oxidation of metal and therefore the formation of corrosion products.
U.S. Pat. No. 5,932,643 issued on Aug. 3, 1999 to Frank J. Kenny teaches coating formulations and thermal transfer ribbons that form printed images containing conductive polymers. The formulations and ribbons include wax, polymer resins, a sensible material and optional solvent. The above is teaching the polymer coatings for their thermal transfer properties. They teach utilizing toxic organic solvents, which have been used for conductive polymers long before this patent was issued. However, no terpenes or terpenoids are taught for use in this patent.
If paint formulations use limonene, pinene, or other terpenes (or terpenoids), as a solvent in a non-water based coating applications instead of traditional high-VOC (volatile organic compound) solvents, it will provide a low-VOC coating application. There is currently no non-toxic, non-chrome, non-metallic, non-aqueous containing coating formulation approved for military application. From the foregoing, it will be appreciated that there is a need in the art for organic terpene non-aqueous based solvent/conducting polymer coating compositions, which is environmentally safe for various types of military and commercial applications. The present invention is directed to overcoming one, or more, of the problems set forth above.